                1. The Field of the Invention        
The present invention relates generally to optical transceiver modules, and more particularly, to loopback and pass-through paths within optical transceiver modules for redirecting input electrical or optical signals.
2. The Relevant Technology
The proliferation and significance of networking technology is well known. The ever-increasing demand for network bandwidth has resulted in the development of technology that increases the amount of data traveling across a network. Advancements in modulation techniques, coding algorithms and error correction have drastically increased rates of this data. For example, a few years ago, the highest rate that data could travel across a network was at approximately one Gigabit per second (Gb/s). This rate has increased ten-fold today where data travels across Ethernet and SONET (Synchronous Optical Network) networks at upwards of 10 Gb/s. For instance, the XFP (10 Gigabit Small Form Factor) Pluggable Module Multi-Source Agreement is directed at transceivers operating at approximately 10 Gb/s.
FIG. 1 illustrates a typical configuration of an optical data transmission system 100. In system 100, a transceiver module 102 is coupled to a network 104 and to a host device 106 such as a media access controller (“MAC”) card or SONET framer. The transceiver module 102 has a receiver 108 that is coupled to network interface 110. The receiver receives an optical input from network 102 and converts into an electrical output signal, which after additional optional processing in transceiver module 102 is relayed to host 106. The transceiver module 102 also has a transmitter 112 that is coupled to network interface 114. The transmitter 112 receives an electrical input from host 106 via additional optional devices in transceiver module 102 and creates an optical signal which is then relayed into network 104 through network interface 114. The optical signal is then passed to transceiver module 120, which may be similar to transceiver module 102. Transceiver module 120 interacts with network 104 and remote host 122 similarly to the manner in which transceiver module 102 interacts with network 104 and host 106. Thus, for example, an electrical signal can be generated by host 106, transmitted to transceiver module 102 and therein converted to an optical signal. The optical signal is relayed at high-speed into and through network 104 and then directed to transceiver module 120. Transceiver module 120 receives the optical signal, converts it into an electrical signal, and passes the optical signal on to remote host 120. Of course, data can be transmitted in the opposite direction or between different transceivers and hosts as well.
Additional devices are typically included in transceiver modules, such as serializer/deserializers (SERDES). Thus, in operation, a serial optical data stream received by the transceiver module 102 is converted to an electrical serial data stream by the receiver 108. This electrical serial data stream is deserialized by SERDES into four channels and transmitted via a parallel bus to host 106 for processing.
A similar deserialization occurs on the transmit side of the transceiver module 102 for the same reasons described above. In particular, a deserialized electrical data stream is transferred from the host 106 to another SERDES via parallel bus. This SERDES serializes this electrical signal. The transmitter 112 converts the serial electrical signal to an optical signal and transmits it onto the network.
One challenge in operation system 100 is in the debugging and maintenance operations of the systems. When data transmission between host 106 and remote host 120 fails, it is often impossible to known precisely where the failure has occurred without sending a network administrator into the field in order to test various links in the system. For example, the network administrator may need to individually isolate and test each of host 106, data fiber or bus 122, transceiver module 102, optical fiber 124, any of a number of devices on network 104, optical fiber 126, transceiver module 120, data fiber or bus 128, and remote host 120. Obviously this can be a daunting and expensive task if the source of the system failure is not quickly detected.
One device or feature that is often used in system diagnostics is a loopback. A loopback is a signal path inserted in the system to route a data signal back to its source or an accompanying device. For example, network administrators often manually tap into a fiber to route a signal back to the source or another detector. If data can be successfully sent from the source and received at a detectable endpoint, a network administrator can verify that the components in the signal path are operating correctly. Through one or more loopbacks along different signal paths a network administrator can identify where in a system a system failure is occurring. In addition to identifying the source of system failures, such loopbacks are also conventionally used to test devices when downstream optical components are not yet connected. For example, it may be desirable to verify that a device is operating correctly by a burn-in process during manufacturing before the device is sold.
However, the cost of sending a network administrator to manually insert a loopback into a networked system each time a test is necessary can be expensive. Similarly, the cost and delay associated with testing devices via temporary loopbacks during device assembly is also undesirable. It would therefore represent an advance in the field of data transmission to provide methods and devices to assist in quickly detecting the source(s) of system failure and to evaluate device reliability without requiring the manual insertion and removal of loopback paths to test each component of an optical system.